［摘要］目的和方法:为了从细胞水平进一步探讨发热时体温正、负调节中枢的调节机制，本实验采用微电极细胞外记录技术，在26只新西兰兔脑腹中隔区（ventral septal area, VSA）记录了温敏神经元单位放电，观察电刺激下丘脑视前区（preoptic anterior hypothalamus, POAH）对致热原IL-1_β作用下兔VSA温敏神经元放电的影响。结果：（1）侧脑室注射的白介素-1_β（IL-1_β）能使VSA热敏神经元放电频率增加，冷敏神经元放电减少，而侧脑室注射等量人工脑脊液（ACSF）对热敏神经元和冷敏神经元的放电均无明显影响。（2）电刺激POAH可反转致热原IL-1_β对VSA热敏神经元和冷敏神经元的上述作用。结论：在致热原作用下的体温调节中，正调节中枢POAH和负调节中枢VSA具有密切的相互作用。

［中图分类号］R364.6 ［文献标识码］A

［文章编号］1000-4718(2000)09-0783-05

Electrical stimulation of POAH alters firing rates of

IL-1_β-treated thermosensitive neurons

in the VSA in rabbits^*

DONG Jun, LU Da-xiang, FU Yong-mei, YAN Liang, TAN Dun-yong, LI Chu-jie^△

(Department of Pathophysiology, Medical College of Jinan University, Guangzhou 510632，China)

［Abstract］ AIM and METHODS: To investigate the functional connection between the preoptic anterior hypothalamus (POAH) and the ventral septal area (VSA) in fever mechanism, the firing rates of thermosensitive neurons in the VSA of 26 New Zealand white rabbits were recorded using extracellular microelectrode technique. RESULTS: The firing rates in both types of thermosensitive neurons in the VSA had no significant changes after intracerebroventricular (icv) injection of artificial cerebrospinal fluid（ACSF）. When interleukin-1_β (IL-1_β) was given (icv), the firing rate of the warm-sensitive neurons was increased significantly and that of the cold-sensitive neurons was decreased remarkably. The effects of IL-1_β on the changes of firing rate in thermosensitive neurons of the VSA were reversed by electrical stimulation of the POAH. CONCLUSION: The roles of positive and negative thermoregulatory centers in the interaction between the POAH and VSA are closely linked during endogenous pyrogen induced fever.

［MeSH］Septal nuclei; Preoptic area; Anterior Hypothalamic area; Body temperature regulation; Interleukin-1;Electrophysiology

［CLC number］R364.6 ［Document code］A

INTRODUCTION

In an earlier report, we showed that the VSA plays a negative-regulation central role in thermoregulation during endogenous pyrogen induced fever. The firing rate of warm-sensitive neurons decreased and that of cold-sensitive neurons increased remarkably in the region of POAH in rabbits after icv. injection of IL-1_β. These responses are appropriate for the increase in heat production and the decrease in heat loss. The effects could be reversed by electrical stimulation of the VSA^［1］, by which the responses are appropriate for the inhibiting heat production and promoting heat loss. In order to further confirm the functional connection between positive and negative regulatory center in fever mechanism, we investigated the effects of electrical stimulation of POAH on firing rates of IL-1_β-treated thermosensitive neurons in the VSA by using extracellular microelectrode technique.

MATERIALS AND METHODS

Surgical procedureThe experiments were performed on 26 New Zealand white rabbits of both sexes weighing 1.5-3.0 kg. The animals were anesthetized with 25% urethane (1.0 g/kg,iv). Supplemental doses of anesthetics were given when required. A midline incision was made on the ventral surface of the neck. The animal breathed spontaneously through a trachea tube and was fixed on a stereotaxic frame (Model IIc Jiangwan). Tubular thermodes (Φ1.2 mm) were placed in A₀、A₅ beyond midline in skull below. Tissue temperature was monitored by a thermistor probe (Φ1.2 mm) placed in a contralateral position symmetrical to that of the recording electrode. Stimulating electrode was insected into the POAH (Stereotaxic coordinates: A_2.5、R_2.5、H₁) , guide cannulae were stereotaxically implanted into the lateral ventricle of rabbits (stereotaxic coordinates: P_4.5、R_4.0、H_6.5). The lateral ventricle infusion was controlled by a microinjector (Shanghai). the environmental temperature was maintained at （22±2）℃during experiment，colon temperature was maintained at 37-39℃.

Electrophysiological recordingSingle-Unit recording was made with a glass microelectrode (＜1 μm tip, DC resistance 8-15 MΩ, filled with 2% pontamine sky blue and acetate sodium 0.5 mol/L at pH 7.3-7.4. The microelectrode was advanced at the speed of 1μm/s by a micromanipulator (SM-21, Narishige) into the VSA (stereotaxic coordinates: A_3-5, R_0-3, H_0-4) until the activity of an extracellular single unit was recorded. Singals were amplified and filtered by a microelectrode amplifier(MEZ-8300, Nihon Kohden). The amplified electrical signals was monitored on an oscilloscope and recorded by a tape recorder (Victor Company of Japan). Spikes were counted by a computer controled Physiological Signal Processing System(NSA-II, NanJing) and displayed in array density histograms.

A monopolar stimulating electrode was constructed from a stainless steel in sect pin (size=00 with a tipe exposure of 500 μm), with the use of a stimulator set to generate monophasic square-wave pulses of 0.5 ms duration, each site was stimulated electrically at a frequency of 50 Hz(30 s, 400 μA).

Experimental protocolsAfter unit-signal activity stabilized 10 minutes,the thermal-response pattern of a unit in H_0-4 was determined by recording the units firing rate as brain temperature was slowly raried twice at a rate of about 0.1-2℃/min by super constant temperature pump from about 34℃ to 42℃, neurons were classfied as warm-sensitive if they had a positive thermal coefficient of at least 0.8 impulse/(s*℃) ［imps/(s*℃)］ or cold-sensitive if they had a thermal coefficient of -0.6 imps/(s*℃) or less. IL-1_β(10 mg/L) (BangDin Company of Beijing, China) was injected (icv). After the icv injection of ACSF 10 minutes, effects of electrical stimulation of POAH on the firing rate of neurons in the VSA were recorded.

Histological assayAt the end of experiment, the dye filled in glass micropippets was diffused out with a negative direct current (20 μA). While the animals were deeply anesthetized, the brain was quickly removed and fixed in 10% formalin. Forzen brain tissue was sectioned in the coronal plane (20-40 μm) after 5-7 d, Histological verification was carried out with reference to Sawyers coordinates^［2］. Data from those electrode tips not in the desired area were excluded.

StatisticsData were expressed as ±s and analyzed using paired Students t test. Differences were considered statistically significant as P＜0.05.

RESULTS

Effects of IL-1_βon the firing rate of warm-sensitive neurons in the VSAIn 14 rabbits, eight spontaneously active single-units in desired area were recorded. After icv injection of IL-1_β, the firing rate of warm-sensitive neurons were increased from (5.